The invention relates to a two-part plastic bottle-cap.
In bottle-caps of the type in question, apart from the problem of maintaining simplicity of construction, there exists the problem of permitting the screwing-on of the caps by means of fast automatic machines; also, there is the problem which is common to all caps which are equipped with a breakable seal, that of guaranteeing the consumer that the bottle has not been fraudulently opened.
One often satisfactory solution to this problem is obtained for example with the cap described in No. GB 2172273 by the same applicant. In that patent a cap is described which is equipped with a first, annular part which is inserted on the neck of the bottle and which exhibits, on its external lateral surface, a plurality of projections arranged in a ring; the second part of this cap comprises a screw-top inferiorly to which an annular breakable seal is attached by means of easily-broken webs. During the assembly phase of the cap, the second part is inserted on the first part in such a way that each strand of the web is arranged between two projections. When the cap is unscrewed for the first time, the web is broken by effect of traction in that the breakable seal, which on first screwing-up has been forced into a position below the lip of the bottle, is not able to follow the cap in its upward movement.
With respect to caps of this type, it has been noted that if the machines used for the first screwing-on of the caps on the bottles are particularly fast, and especially if the user of the caps allows wide margins with regard to the nominal diameter of the bottlenecks, the following can happen: if the bottlenecks are much wider than the nominal diameter, the web is broken on first screwing-on; if the neck is much narrower than the nominal diameter, there is the possibility of fraudulent opening due to the poor level of interference between the bottleneck and the cap.
Evidently it is not possible to strengthen the webs by thickening them, nor increase interference between the cap and the bottleneck; each of these solutions would address one of the problems while neglecting the other. It is therefore necessary to adopt web thicknesses and interference values which represent a compromise with regard to the solution of the above-described problems, even if by so doing, in the cases where the real diameter of the bottle is near to the maximum or minimum values permissible, one or the other of drawbacks may be encountered.
Another drawback encountered in caps of this type is that of the possibility of unscrewing the cap fron the bottle without breaking the webs, by levering beneath the cap itself using an appropriater tool. Although this operation is rather difficult to perform, the very fact that it is possible means that protection against fraudulent opening cannot be guaranteed.
Aim of the present invention is to eliminate the above-described drawbacks by providing a cap which is of simple construction, which permits of correct functioning with regard to both the first screwing-on phase and the unscrewing phase, with bottles that allow of an adequate tolerance of the nominal diameter and which is not removable from the bottleneck without one of its parts breaking.
An advantage of the present cap is that it permits of obtaining the desired results without any increase in production costs and without any further application complications.